Vitamin Deficiencies on GLP-1s: What to Watch For

GLP-1 medicines such as semaglutide, tirzepatide, and liraglutide work by lowering your appetite. Eating much less is how they help you lose weight, but it also means you may not get enough vitamins and minerals unless you plan your meals. Because you are eating smaller amounts, every bite needs to count.

Why Eating Less Can Leave You Short

Your body's need for vitamins and minerals does not drop when your appetite does. When daily intake falls below about 1,200 calories for women or 1,800 calories for men, it becomes hard to get everything your body needs from food alone.[1]

Food quality matters as much as quantity. In a two-year trial of moderate calorie reduction with intensive support, diet quality improved and nutritional adequacy was maintained.[6] Smaller meals can still cover your needs if they are built from nutrient-rich foods.

The Nutrients Most Likely to Fall Short

Focus on food first, and talk to your clinician about whether a supplement is right for you.[1][2]

Nutrient	Why it matters	Good food sources
Vitamin D and calcium	Bone strength	Dairy, fortified milk, leafy greens, sardines
Iron	Energy, healthy blood	Lean meat, beans, spinach (pair with vitamin C)
Vitamin B12	Nerves, blood, energy	Meat, fish, eggs, dairy, fortified cereals
Folate	Blood; important in pregnancy	Leafy greens, beans, citrus
Thiamine (B1)	Nerves and brain	Whole grains, pork, legumes
Magnesium and potassium	Muscles, heart, nerves	Nuts, seeds, beans, bananas, leafy greens
Zinc	Immune health, wound healing	Meat, shellfish, seeds, beans
Vitamins A, C, E, and K	Vision, immunity, skin, healing	Colorful fruits and vegetables, nuts, oils
Protein	Muscle, skin, immune health	Eggs, fish, poultry, dairy, beans

Protein is not a vitamin, but it is the nutrient people on these medicines most often miss. Targets and food amounts are in how much protein you need on a GLP-1.

A Special Note on Thiamine (Vitamin B1)

Your body stores only about a 1 to 3 week supply of thiamine. If you have vomiting or very low intake for more than a week, tell your clinician promptly. Low thiamine can cause serious nerve and brain problems.

This is rare. A 2026 review found six published case reports in people taking semaglutide for obesity, and every one followed prolonged stomach symptoms and substantial weight loss.[7] Confusion, balance problems, or vision changes need prompt medical care.

About Supplements

• A daily multivitamin. Many people on these medicines benefit from a once-daily complete multivitamin-and-mineral that includes iron, zinc, B12, and folic acid, especially when eating very little.[2][3]
• Single nutrients. Your clinician may also recommend vitamin D, calcium, or B12 separately, or check blood levels first.[5]
• No high doses on your own. Do not start high-dose supplements without guidance from your clinician.

If you could become pregnant, folate matters even more. See GLP-1s and pregnancy.

A Simple Plate for Small Meals

• Half the plate: vegetables and fruit (berries, leafy greens, broccoli, tomatoes, carrots, peppers)
• One-quarter: lean protein (fish, poultry, eggs, beans, tofu)
• One-quarter: whole grains (oats, quinoa, brown rice, whole-grain bread)
• A little healthy fat: olive oil, avocado, or nuts, which help your body absorb certain vitamins

Foods to enjoy: fruits, vegetables, whole grains, yogurt and other dairy, eggs, fish, poultry, beans, nuts and seeds, olive and avocado oil.

Foods to limit: sugary drinks, sweets and salty snacks, refined or white grains, fast food, and red or processed meats.[1]

A fuller list is in what to eat on a GLP-1.

Easy, High-Nutrition Meal Ideas

• Greek yogurt topped with berries, chia seeds, and a few nuts
• Scrambled eggs with spinach and a slice of whole-grain toast
• Cottage cheese with sliced fruit
• Grilled chicken or salmon with roasted vegetables and quinoa
• Lentil or bean soup with a side salad
• A protein smoothie (milk or soy milk, protein powder, banana, peanut butter)
• Tofu or chicken stir-fry with mixed vegetables and brown rice

When Your Appetite Is Very Low

• Eat small meals more often (3 to 6 times a day), and try not to skip meals entirely.
• Start each meal with the protein food, before your appetite fades.
• If solid food is hard, try soft or blended foods, soups, and smoothies. A shake with at least 20 grams of protein per serving is an easy way to catch up.
• Choose bland, cool, or room-temperature foods if smells bother you.

The Basics That Support Good Nutrition

• Fluids: about 8 to 12 cups (2 to 3 liters) a day, mostly water. See hydration and electrolytes on GLP-1s.
• Fiber: build up slowly to about 25 grams a day from oats, fruits and vegetables, beans, kiwifruit, prunes, flaxseed, and chia seeds. See constipation on GLP-1s.
• Strength exercise: 2 to 3 times a week, plus about 150 minutes of moderate activity.[4] See preserving muscle on GLP-1s.

When to Call Your Clinician

Contact your healthcare team if you notice:

• Unusual tiredness, muscle weakness, or hair loss
• Flaky or itchy skin, slow-healing cuts, or easy bruising
• Vomiting, or being unable to keep fluids down, for more than a day or two
• Confusion, balance problems, or vision changes (seek care promptly)
• Trouble eating enough to maintain even small, regular meals

Tiredness and hair shedding have other common causes on these medicines too. See fatigue on GLP-1s and hair loss on GLP-1s.

The Short Version

Smaller meals need to be nutrient-rich meals. Build them around protein, vegetables, fruit, and whole grains, ask your clinician about a daily multivitamin, and report prolonged vomiting or very low intake early. A registered dietitian can tailor a plan to you.